Internal combustion engines, including diesel engines, subject piston top ring seals to high pressures and temperatures that cause wear on the seals and on the cylinder walls of the engine. Piston ring seals are generally seated in a groove formed in the outer circumference of the piston and perform at least two functions to ensure efficient operation of the engine. First, during the power cycle, the ring seals prevent gases under high pressure from bypassing the piston. Thus, maximum driving force is applied to the piston. Second, on the return stroke, the ring seals prevent lubricants from entering the combustion chamber. If the ring seals fail to perform efficiently, the engine will not develop the maximum power due to “blow-by” on the power cycle. Additionally, if the ring seals leak during the return stroke, lubricants will enter the combustion chamber, thereby reducing combustion efficiency and increasing air pollution by way of the exhaust cycle. Generally, the ring seal provides the interface between the piston and the cylinder wall. Thus, reduced friction is desired. Conventional top ring seals experience radial excursion during high-pressure periods in the combustion cycle. More particularly, the high-pressure gases leak behind the ring seal and force an outwardly radial excursion of the ring seal against the cylinder wall. The result is reduced efficiency of the lubricating film, and thus the film does not fully protect the ring seal and the cylinder wall from direct frictional contact. The result is excessive wear of both the ring seal and the cylinder wall.
Because of this, there is a need for a piston seal that produces lesser radial forces between the ring seal and the cylinder wall during maximum chamber pressures. Use of such a piston seal results in improved sealing, reduced wear and it provides an efficient lubricant action throughout the piston stroke.